GB2151797A

GB2151797A - Gas metering apparatus

Info

Publication number: GB2151797A
Application number: GB08431543A
Authority: GB
Inventors: Tronje Von Dem Hagen; Carl Friedrich Wallroth
Original assignee: Draegerwerk AG and Co KGaA
Current assignee: Draegerwerk AG and Co KGaA
Priority date: 1983-12-16
Filing date: 1984-12-13
Publication date: 1985-07-24
Also published as: US4651730A; DE3345585C1; ATA209184A; JPH0219410B2; CH664087A5; FR2556590B1; SE8404529D0; GB8431543D0; AT392006B; GB2151797B; SE459557B; JPS60151518A; SE8404529L; FR2556590A1

Description

1 GB 2 151 797 A 1

SPECIFICATION

Gas metering apparatus The invention relates to a gas metering apparatus, for example for use with medical equipment.

British Patent Application No. 8317106 discloses a gas metering apparatus comprising: a gas supply line, for connection to a supply of gas; a first chamber for gas connected to the supply line; switch 75 means; a second chamber for gas connectible selectively to the supply line and the outlet line by means of the switch means; and sensing means, for sensing the pressure difference (A p) between the first and second chambers, the switch means being controlled in response to Ap, the arrangement being such that, with the gas supply line connected to a supply of gas, and with the switch means in a first position, gas flows from the supply to the first and second chambers, and not to the outlet, until chambers are filled to the admission pressure po and A p reaches a value of zero. After a predeter mined delay, the switch means achieves a second position in which gas flows from the second cham ber to the outlet line until A p achieves a predeter mined value which causes the switch means to be returned to the first position, in which the second chamber is refilled to the admission pressure po.

A buffer is connected: to the gas supply line, downstream of the supply of gas; to the first chamber; and to the second chamber when the switch means is in its first position, a choke being arranged between the buffer and the first chamber.

The sensing means is in the form of a differential pressure monitor which is connected to the first and 100 second chambers by respective gas lines.

The choke serves to prevent instantaneous press ure fluctuations in the first chamber, which serves as a pressure reference chamber.

The quantity of metered gas leaving the outlet depends on the volume of the second chamber, the pressure difference Ap of each switching cycle and the switching frequency of the cycles. However, because of the pressure difference between the first and second chambers when the second chamber is 110 emptying, the pressure in the first chamber affects, via the sensing means, the metered volume of gas at the outlet. In addition, the regulating range is limited, for example, by the given volume of the second chamber. In order to extend the regulating range, metering equipment may contain several independent such metering apparatus of varying design together with a common control unit. Adjust ment to the desired gas flow is then made by selecting the appropriate metering apparatus. 120 According to the present invention there is pro vided a gas metering apparatus comprising: a gas supply line, for connection to a supply of gas at a first pressure (PJ; a gas outlet line, forthe outlet of metered gas; a first chamber for gas connected to the supply line; switch means; a second chamber for gas connectible selectively to the supply line and the outlet line by means of the switch means; valve means, operable between an open and a closed position, disposed in the outlet line; and sensing means, for sensing the pressure difference (Ap) between the first and second chambers, the switch means and the valve means being controlled in response to Ap, the arrangement being such that, with the gas supply line connected to a supply of gas, with the switch means in a first position, and with the valve means in its closed position, gas flows from the supply to the first and second chamber, and not to the outlet, the first pressure (PJ prevaifin gin the first chamber, until Ap achieves a predetermined value which causes the switch means to achieve a second position and, after a predetermined delay, the valve means to achieve its open position so that gas flows from the second chamber to the outlet line until Ap achieves another predetermined value which causes the valve means to be returned to the closed position, and the switch means to be returned to the first position.

Preferably the apparatus further includes a third chamber which is connected: to the gas supply line, downstream of the supply of gas; to the first chamber; and to the second chamber when the switch means is in its first position; there being first choke means arranged between the third chamber and the first chamber, the third chamber comprising a buffer.

Athird choke means may be arranged between the second chamber and the first-mentioned switch means.

The apparatus may further comprise a second switch means and a fourth chamber, the fourth chamber being connectable byway of the second switch means to a connection line between the third choke means and the first switch means, the second switch means being controllable by a control unit. A temperature sensor may be disposed in the third chamber.

In one embodiment there are connected into the outlet line a pilot valve constituting the valve means and, subsequently an outlet buffer and an outlet throttle, or choke means, and a control unit controls the switch means and the pilot valve in such a way that, on starting, with the gas supply line connected to a supply of gas, with the switch means in a first position, and with the valve means in its closed position, gas flows from the supply to the first and second chambers until the admission pressure P,, obtains in the first and second chambers which causes the switch means to achieve a second position so that, when the valve means is switched to its open position, gas can flow from the second chamber to the outlet until Ap achieves a first predetermined value to initiate a metering cycle by causing the switch means to achieve its first position and the valve means to achieve its closed position in which gas can flow from the supply to the measuring chamber until Ap achieves a second predetermined value which causes the switch means to switch into its second position so that when the valve means is switched to its open position, gas can flow from the second chamber to the outlet until Ap achieves its first predetermined value to reinitiate the metering cycle.

The advantages achieved by means of the inven- tion lie in the incorporation of the pilot valve in the 2 GB 2 151797 A 2 outlet line. This makes the switching pressure, hence the pressure difference for switching during the metering cycles, independent of the admission pressure P.. The first and second predetermined values for the pressure differences, P, and P2, corresponding to the respective switching state of the switch means and of the pilot valve, eliminate in practice, over each cycle, P. from the outlet pressure. This occurs because the pressure differences 10 are given bythefollowing:

A P,= P. - P, A P2 = Po - P2 where P, is the admission pressure, practically the same in both cases, P2 is the pressure to which the measuring chamber is filled with the switch means in the first position, and P, is the pressure in the measuring chamberjust before the pilot valve switches back to its closed position.

Thus, embodiments of the invention provide a gas metering apparatus, in particular for medical devices, which, using electrical control signals, can be used independently of admission pressure and of outlet pressure over a wide metering range.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, byway of example, to the accompanying drawings, in which:

Figure 1 shows one embodiment of an apparatus in accordance with the present invention; and Figure 2 is a graph of pressure versus time illustrating operation of the apparatus.

As shown in Figure 1, a metering unit 3 is supplied with gas from a gas source 1 via a pressure reducer 2 and delivers metered gas via an outlet 4 to a consumer. A control unit 5 controls the metering unit 3 on the basis of signals which it receives from the metering unit 3 and from its rated value input 6. The setvalues, and any malfunctions, are indicated on an indicator 7.

In the metering unit 3 a buffer 8 is connected to the pressure reducer 2 via a pipe line, and a pressure chamber 10 is connected to the buffer 8 via a choke 9.

Switch means in the form of a switch valve 11 enables a measuring chamber 13 to be connected, via a further choke 12 and connection line 21, to the buffer 8 in a first position of the switch valve 11; and to the outlet 4 via an outlet line 14 in a second 115 position of the switch valve 11.

A control valve 15, operable between closed and open positions, an outlet buffer 16 and an outlet choke 17 are connected in that order in the direction of flow in the outlet line 14.

A differential pressure sensor 18 is connected via respective gas lines to the pressure chamber 10 and to the measuring chamber 13; and via an electrical signal line to the control unit 5. The switch valve 11, and control valve 15, are controlled electrically by the control unit 5, in response to signals from the sensor 18. The metering range may be extended by means of an additional chamber 19 which can be connected to the connection line 21 between the switch valve 11 and the measuring choke 12 via an additional valve 20.

The control unit 5 controls byway of electrical signals the additional valve 20.

Atemperature sensor 22 in the inlet buffer 8 allows temperature observation of the inlet gas from the gas source land, byway of the control unit 5, a] lows correction to be made in order to make the metering more accurate.

During operation, and with reference to Figure 2, when the metering apparatus is switched on for the firsttime, the switch valve 11 is in its first position and gas flows from the gas source 1 via the pressure reducer 2, the buffer 8 and the switch valve 11 into the pressure chamber 10 and 13 are filled until they reach the admission pressure P.. When the pressure P. is reached, the switch valve 11 switches over into its second position. As the valve 15 is still closed, however, no gas may escape from the chamber 13 to the outlet 4. Not until the control valve 15 is switched into its open position can the cas flow out of the chamber 13 to the outlet 4. Accordingly valve 15 is opened and the gas from the measuring chamber 13 then flows via the control valve 15, outlet buffer 16 and outlet choke 17, to the consumer and the pressure in the measuring chamber 13 fails until there obtains in the chamber 13 a prescribed first pressure value P, which differs from the pressure P, in the chamber 10 by the amount AP1. When the predetermined pressure difference Ap is reached between the admission pressure P. and the operating pressure in the measuring chamber 13, where AP, = P. - P,, this is determined by the differential pressure sensor 18, and the control unit 5 causes the control valve 15 to close, and subsequently switches the switch valve 11 into its first position. With this, the measuring chamber 13 is filled by gas flowing from the gas supply 1 until the pressure in chamber 13 has increased to a second predetermined value P2 which differs from the pressure P. in chamber 10 by the amount kP2 (1P2 Po - P2). When pressure P2 is reached, the pressure difference 11P2 is sensed by the sensor 18, and the control unit switches the switch 11 into its second position again, as a result of which the gas lines 14 and 21 are interconnected. After a predetermined delay, the control valve 15 is switched over into its closed positioned, as a result of which the gas is able to escape from the measuring chamber 13 to the outlet 4, and hence to the consumer. When the pressure fails to the pressure P, again, the control valve 15 is closed and the switch valve 11 switched to its first position to begin the metering cycle again. The predetermined pressure difference 11P2 is determined by the rated value input 6. The additional chamber 19 can be connected to the line 21 in response to the rated value input 6 to effectively increase the volume of the measuring chamber. With this, different gas volumes which result as total f low equal to = (P2 - P1) x measuring volume x number of cycles may be established.

According to the desired operation the chambers 10 and 13 are thus filled jointly to the admission pressure P. the first time only, that is on starting. Subsequently during the measuring cycle, the pressure P., whereas the pressure in the measuring chamber 13 may fluctuate between the variable 3 GB 2 151797 A 3 pressure values P, and P2. The predetermined delay, t variable for opening the control valve 15 provides the user with the possibility of varying the dosing or metering frequency.

This operation compares favourably with the apparatus of British Patent Application No. 8317106 in which the reference pressure is always the supply pressure P.. Therefore a drop in pressure in the measuring chamber had to be measured as a difference in respect of the supply pressure. In the case of the metering apparatus according to the invention, only the fluctuations in pressure in the measuring space 13 between the filling process and the emptying process are measured. This produces substantially more accurate metering than is possible using the gas metering apparatus of Application No.8317106.

Claims

1. A gas metering apparatus comprising: a gas supply line, for connection to a supply of gas at a first pressure (P.); a gas outlet line, for the outlet of metered gas; a first chamber for gas connected to the supply line; switch means; a second chamberfor gas connectible selectivelyto the supply line and the outlet line by means of the switch means; valve means, operable between an open and a closed position, disposed in the outlet line; and sensing means, for sensing the pressure difference (Ap) between the first and second chambers, the switch means and the valve means being controlled in response to Ap, the arrangement being such that, with the gas supply line connected to a supply of gas, with the switch means in a first position, and with the valve means in its closed position, gas flows from the supply to the first and second chamber, and not to the outlet, the first pressure (PO) prevailing in the first chamber, until Ap achieves a predetermined value which causes the switch means to achieve a second position and, after a predetermined delay, the valve means to achieve its open position so that gas flows f rom the second chamber to the outlet line until Ap achieves another predetermined value which causes the valve means to be returned to the closed position, and the switch means to be returned to the first position.

2. An apparatus as claimed in claim 1, further including a third chamber which is connected: to the gas supply line, downstream of the supply of gas; to the first chamber; and to the second chamber when the switch means is in its first position; there being first choke means arranged between the third chamber and the first chamber.

3. An apparatus as claimed in claim 2, wherein the third chamber comprises a buffer.

4. An apparatus as claimed in any preceding claim, wherein a second choke means is arranged in the gas outlet line.

5. An apparatus as claimed in any preceding claim, wherein a pressure reducer is arranged in the gas supply line upstream of the first chamber, and of the third chamber when present.

6. An apparatus as claimed in any preceding claim, wherein a third choke means is arranged between the second chamber and the firstmentioned switch means.

7. An apparatus as claimed in any preceding claim, further comprising a second switch means and a fourth chamber, the fourth chamber being connectible by way of the second switch means to a connection fine between the second chamber and the first switch means, the second switch means being controllable by a control unit.

8. An apparatus according to any preceding claim, further comprising a temperature sensorfor sensing the temperature of gas from the supply of gas.

9. An apparatus as claimed in claims 2 and 8, wherein the temperature sensor is disposed in the third chamber.

10. An apparatus as claimed in any preceding claim wherein a fifth chamber comprising a buffer is connected in the gas outlet line.

11. A gas metering apparatus substantially as hereinbefore described with reference to, and as shown in Figure 1 of the accompanying drawings.

Printed in the U K for HMSO, D8818935,6185,7102. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.